4 water resources and climate in the future

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Last modified 13 Apr 2011, 07:27 PM

4. Water
Resources And Climate in The Future

It is expected that water resource
problems associated with desertification, flooding, erosion and sediment transport, water
contamination, over-exploitation of aquifers, etc., will become more acute in the future,
and this will make the sustainable development of water resources even more difficult.
Modifications to the climatic system will merely serve to complicate matters.

The water cycle plays an extremely
important and reciprocal role in the climatic system, both conditioning the climate and
being affected by it. Changes in precipitation can bring about changes not only to the
runoff magnitude and temporality, but also to the frequency and intensity of storms and
droughts. Temperature changes undoubtedly cause alterations to the evapotranspiration,
soil moisture and seepage to the deepest layers. Such changes in the surface water-content
modify the vegetation cover, which brings about a chain reaction, affecting cloud
formation, the Earth's albedo and precipitation.

Studies carried out into the impact
of possible climatic change on water resources in semi-arid zones should be pointed out by
way of example. According to the first report on scientific evaluation of the IPCC (1992),
a temperature increase of 1º C to 2º C, together with a 10% precipitation reduction,
could lead to a 40% to 70% reduction in renewable resource. Furthermore, a temperature
increase could cause snow to melt earlier, increasing the winter runoff and reducing the
thawing processes in spring and summer. Even in the areas where precipitation increases,
the greater evaporation could lead to lower runoff rates.

A variation in the risk and
intensity of droughts is the most serious negative impact of climatic change on water
resources. A reduction in water availability could lead to desertification in zones where
the balance is particularly fragile.

Climatic change can have
considerable repercussions on the flood regime. The predicted variation in storm magnitude
and frequency would give rise to a spectacular increase in runoff in short periods of
time, which would aggravate the already catastrophic effects of flooding, thus making it
necessary to review present techniques for water resources estimation, prevention,
prediction and management.

It is only to be expected that a
worsening in the summer would adversely affect the water quality and it would increase
salinity in the water and the soil. Water scarcity would make effluent dilution more
difficult, causing, amongst other phenomena, a further increase in reservoir
eutrophication. The scarcity of the resource ought to lead to the deployment of wastewater
for other purposes.

The impact on aquifers of potential
climatic change would take the form of a reduction in natural recharge (renewable
resource), giving rise to a reduction and eventual disappearance of natural outlets
(rivers, springs, wetlands etc.). Furthermore, the possibilities for management would
become reduced and more complicated, being excessively concentrated on specific aquifers,
with the evident risk of over-exploitation. A reduction in the capacity of the resources
to be renewed would cause a lowering of water quality and a drop in the groundwater table
which, in coastal areas would lead to an increase in seawater intrusion; the latter
problem could be further aggravated by a rise in the sea level.

The degradation and even
disappearance of vegetation cover, especially that of the woodland type, together with an
increase in torrential rain and a reduction in soil moisture, would increase erosion and
soil loss, thereby reducing the useful life of the reservoirs by causing them to silt up,
all of which would have a negative effect on harnessing water resources.

As a result of the aforementioned,
an attempt must be made in the near future in order to obtain a greater insight into the
possible effects of climate change upon the quantity and quality of water resources, on
the water requirements of the various human activities and the availability of this
particular resource, especially in the semi-arid zones which are the subject of this
report.

In Portugal, according to the First
European Climate Assessment and with the help of ESCAPE model, it was possible to predict
the following changes between 1990 and 2050:

In Sardinia, water resources have
diminished due to lower precipitation. For example the water collected in the Flumendosa
reservoir has dropped to 30%. Average discharge over the last twenty years is roughly
60-65% of the average for the previous 50 year period and over the last nine years, it is
only 45%.

In Spain, studies have not thus far
been made to assess the possible effect of changes in precipitation and evapotranspiration
on water resources. However, guidelines for these studies are now being prepared by CEDEX
for the General Directorate of Hydraulic Works and Water Quality.